The spread of "shall issue" laws
No Lawyers -- Only Guns and Money-- has an interesting graph. To abbreviate ... from 1986 to present, "shall issue" went from about 10% of the US population to over 60%, while "no issue" of CCW permits fell from 33% to about 5%. Another interesting trend is that States tend to go from "no issue" to "shall issue." Arizona did that in a way, going from no issue to shall issue to no permit required. It never had a "may issue" stage.